Dual-mode active rear-wheel steering device based on differential principle

This application claims the benefit of priority from Chinese Patent Application No. 202210001614.6, filed on Jan. 4, 2022. The content of the aforementioned application, including any intervening amendments thereto, is incorporated herein by reference in its entirety.

This application relates to automotive steering, and more particularly to a dual-mode active rear-wheel steering device based on differential principle.

Compared with traditional front-wheel steering, four-wheel steering can also control the rear-wheel steering in addition to controlling the front-wheel steering. The four-wheel steering system features an ability to independently control a lateral force of rear wheels. The rear-wheel compliance steering technique, such as programmed self-steering system (PSS) of Citroen, realizes the rear-wheel passive steering through the lateral deformation of a suspension, which improves the steering performance of vehicles under different conditions. Whereas, this technique cannot actively regulate the steering angle of the rear wheels, and is thus limited in the vehicle performance improvement. By comparison, the active rear-wheel steering technique can actively control the rear-wheel steering angle to adjust the driving state according to vehicle state information fed back during driving (such as speed, yaw rate and sideslip angle), leading to flexible low-speed steering, stable high-speed driving and safe braking. Due to the presence of the rear-wheel steering control, the four-wheel steering vehicles are superior to traditional front-wheel steering vehicles in vehicle performance, steering response, and driving safety and control.

In view of the great potential in improving the vehicle steering and active safety, the active rear-wheel steering has been extensively investigated, and applied to various commercially-available high-end models. For example, Cadillac CT6 uses an active rear-wheel steering system (ARS), in which a servo motor cooperates with a multi-link suspension to reach a rear-wheel steering angle of up to 3.5°. Nevertheless, the active rear-wheel steering is achieved by a single actuator through a steering mechanism, that is, steering angles of two rear wheels are determined by the rear-wheel steering trapezoid mechanism, and are not decoupled from each other. The active rear-wheel steering system developed by ZF Friedrichshafen AG adopts two drive motors respectively at left sand right sides to independently control steering angles of the two rear wheels, enabling the steering angle decoupling of the two rear wheels. This active rear-wheel steering system has been equipped in Porsche 911Turbo and 911GT3 to drive the two rear wheels to steer in the same direction and achieve a maximum rear-wheel steering angle of 3°.

The rear-wheel steering system can improve the steering performance of vehicles, enhancing the maneuverability under low-speed steering conditions and steering stability under high-speed driving conditions. Moreover, the active rear-wheel steering technique also can be used to enhance the directional stability during braking by controlling the two rear wheels to steer with opposite direction simultaneously. However, this technique is merely applied to Acura's precision all-wheel steering (PAWS) system, in which two distributed actuators are employed to respectively control the rear wheels to simultaneously turn inward by an angle, improving the directional stability when braking at high speed.

Though the Acura's PAWS system can improve the steering performance when cornering at different speed and directional stability when braking at high speed, the two independent steering motors will lead to high cost and poor system reliability. More seriously, once one steering motor fails and the other works normally, the vehicle will experience unstable and uncoordinated steering, which will easily cause an accident.

In order to overcome the above-mentioned deficiencies in the existing rear-wheel steering techniques, the present disclosure provides a dual-mode active rear-wheel steering device based on differential principle, which allows the two rear wheels to deflect in the same or opposite direction based on the differential principle and selective control of an electromagnetic clutch. Therefore, this rear-wheel steering device has two operation modes, namely steering mode and braking mode. The steering of the two rear wheels is controlled by a single mechanism, which brings great reliability, and effectively decline the failure risk caused by excessive actuators. Furthermore, the steering system has simple structure, easy assembly and disassembly and high coaxial compactness, and thus is suitable for the practical application.

Technical solutions of this application are described as follows.

This application provides a dual-mode active rear-wheel steering device, comprising:

In some embodiments, the housing assembly comprises a first housing and a second housing;

the first housing is configured to accommodate the speed-reduction mechanism and a first end of the motion conversion mechanism; and

the second housing is configured to accommodate the differential mechanism assembly and the second electromagnetic clutch.

In some embodiments, the speed-reduction mechanism comprises an input gear and an output gear;

In some embodiments, the differential mechanism assembly comprises the differential housing, a first half shaft gear, a second half shaft gear, a universal joint, a planetary gear, a first thrust gasket, a second thrust gasket and a spherical gasket;

In some embodiments, the first electromagnetic clutch comprises a clutch housing, a first electromagnetic coil, an armature, a torque adjusting ring, a spring, a spring locating ring and a friction sheet;

In some embodiments, a first wire is directly connected to the first electromagnetic coil of the first electromagnetic clutch from an outside of a clutch housing of the first electromagnetic clutch; and

In some embodiments, the second electromagnetic clutch comprises a clutch housing, a second electromagnetic coil, an armature, a torque adjusting ring, a plurality of springs, a spring locating ring and a friction sheet;

In some embodiments, a second wire is connected to the second electromagnetic coil of the second electromagnetic clutch from a slip ring at an end of the clutch housing of the second electromagnetic clutch going through the housing assembly; and the second wire is configured to supply electric power to the second electromagnetic clutch; and

In some embodiments, the motion conversion mechanism comprises a first motion conversion mechanism and a second motion conversion mechanism; and the first motion conversion mechanism is configured to control a steering angle of the rear wheel at the first side, and the second motion conversion mechanism is configured to control a steering angle of the rear wheel at the second side.

In some embodiments, the first motion conversion mechanism comprises a first lead screw, a first steering tie rod and a dust-proof cover;

In some embodiments, the second motion conversion mechanism comprises a second lead screw and a second steering tie rod;

In some embodiments, the first lead screw and the second lead screw are the same in parameters except rotation direction, and a rotation direction of the first lead screw is opposite to a rotation direction of the second lead screw.

In some embodiments, the differential mechanism assembly is configured to be switched between two modes under control of the first electromagnetic clutch and the second electromagnetic clutch; and motions of the differential housing, the first half shaft and the second half shaft satisfy the following equation:=2;

In some embodiments, when the first electromagnetic clutch and the second electromagnetic clutch are both in the de-energized state, the differential housing and the housing assembly are fixedly connected by the action of the first electromagnetic clutch, such that the rotation speed of the differential housing n=0 rad/s, that is, the rotation speed nof the first half shaft and the rotation speed nof the second half shaft satisfy the following equation:=0;

In some embodiments, when the first electromagnetic clutch and the second electromagnetic clutch are both in the energized state, the differential housing and the housing assembly are disconnected, such that the differential housing is rotatable; the differential housing and the second half shaft are fixedly connected, such that motions of the differential housing, the rotation speed of the first half shaft and the rotation speed of the second half shaft satisfy the following equations:=2; and;

In some embodiments, when first electromagnetic clutch is in the de-energized state and the second electromagnetic clutch is in the energized state, the differential housing, the housing assembly and the second half shaft are fixedly connected, such that the rotation speed of the differential housing, the rotation speed of the first half shaft and the rotation speed of the second half shaft satisfy the following equation:=0rad/

Compared to the prior art, this application has the following beneficial effects.

1. The dual-mode active rear-wheel steering device provided herein adopts a series of electro-mechanical actuators to control the vehicle operation under the steering mode and the braking mode. Compared with the existing active rear-wheel steering devices that only improves steering characteristics during the steering operation, the dual-mode active rear-wheel steering device provided herein can also improve the braking performance and safety of the vehicle.

2. This application employs a modified differential and two electromagnetic clutches to realize the dual-mode steering. Moreover, the gear is integrally formed with the half shaft to simplify the structure and reduce the system volume. The split-type housing facilitates the disassembly and maintenance.

3. This application enables two rear wheels to steer in the same direction under common steering conditions when two electromagnetic clutches are in a de-energized state, which contributes to less energy consumption under the steering mode. Meanwhile, since the steering operation is dependent on the mechanical structure, the system reliability is enhanced.

4. Compared to the strategy adopting two motors to respectively drive the two rear wheels, this application merely adopts a single motor to realize two operation modes, reducing the system complexity, as well as avoiding uncoordinated steering action in the case that one motor works normally while the other fails.

5. The self-locking of the dual-mode active rear-wheel steering device is controlled by two electromagnetic clutches, thereby avoiding shaking and vibration of rear wheels when travelling on uneven roads or suffering impact of obstacles, and improving the overall safety and reliability.

Technical solutions of the present disclosure will be described below with reference to the accompany drawings and embodiments to facilitate the understanding.

Illustrated inis a dual-mode active rear-wheel steering device based on differential principle, which includes a steering angle control motor, a speed-reduction mechanism, a differential mechanism assembly, a first electromagnetic clutch, a second electromagnetic clutch and a motion conversion mechanism. A housing assemblyis mounted on a rear axle subframe of a vehicle through a mounting base. An axis of the housing assembly is perpendicular to an xy-plane in a vehicle coordinate system. The steering angle control motoris mounted on the housing assemblythrough a mounting flange. An axis of the steering angle control motoris parallel to an axis of the housing assembly. A motor shaftis connected to an input shaftthrough a shaft coupling. A pinion gearis arranged on the input shaftby a key connection, such that power is transferred through the pinion gear to a gear wheel integrally formed by a first half shaftin the differential mechanism assembly, so as to realize deceleration and torque increase. Under a steering mode, the first electromagnetic clutchand the second electromagnetic clutchare in a de-energized state, and a differential housingof the differential mechanism assembly is fixed to the housing assembly, that is, the differential housingis fixed, and a rotation speed n=0 rad/s. A second half shaftis disconnected from the second electromagnetic clutchfixed on the differential housing, thus the second half shaftis capable of free rotation. Therefore, according to a differential principle n+n=2*n, the first half shaftand the second half shafthave the same rotation speed with opposite rotation direction. The first half shaft, the second half shaft, a first lead screwand a second lead screwform an inner cyclical ball-lead screw-nut pair. The first lead screwand the second lead screware the same in parameters expect a rotation direction, that is, a rotation direction of the first lead screwis opposite to a rotation direction of the second lead screw. The inner cyclical ball-lead screw-nut pair is configured to convert a rotational motion of the steering angle control motorinto a linear motion. The first lead screwand the second lead screwmove in the same direction and have equal motion displacement. Regarding the traditional vehicles with front-wheel steering, a rear suspension is provided with a rear-wheel toe-in control arm to adjust a toe-in angle of each rear wheel. In view of this, the connection between the rear-wheel toe-in control arm and the frame can be replaced with the connection between the rear-wheel toe-in control arm and an output end of the motion conversion mechanism through a ball pin, such that the linear motion of the output end of the motion conversion mechanism, which is also the lead screw of the inner cyclical ball-lead screw-nut pair, drives two rear wheels to perform active steering, therefore, the vehicles with front-wheel steering can perform active rear-wheel steering. Meanwhile, since the rear wheels participate in motion of steering system and suspension system, pin-shaft connection between control arm and wheels is changed to ball-pin connection between a steering tie rodand a steering knuckle arm, so as to prevent motion interference between steering motion and suspension motion. In consequence, a first output end of the motion conversion mechanism, namely the first lead screw, is connected to a steering tie rodof a rear wheelat a first side; and a second output end of the motion conversion mechanism, namely the second lead screw, is connected to a steering tie rodof a rear wheelat a second side. The linear motion of the first lead screw and that of the second first lead screw drive the tie rod to perform a linear motion, such that the steering knuckle arm rotates around a main pin, and the two rear wheels can steer.

As shown in, the dual-mode active rear-wheel steering device includes the steering angle control motor, the speed-reduction mechanism, the differential mechanism assembly, the first electromagnetic clutch, the second electromagnetic clutch, the motion conversion mechanism and the housing assembly. The housing assemblyis a sectional type housing, including a first housing, a second housingand an end cover. The first housingis configured to accommodate a motor shaft, an input shaft, a shaft coupling and the speed-reduction mechanism, in which the shaft coupling is configured to connect the motor shaft and the input shaft. The second housingis configured to accommodate the differential mechanism assembly and the second electromagnetic clutch. The end coveris configured to accommodate the motion conversion mechanism. The first housing, the second housingand the end coverare successively connected through a first connecting screw, a second connecting screw, a third connecting screwand gaskets corresponding to the three connecting screws.

The steering angle control motor is configured to drive rear wheels to steer and control a steering angle of the rear wheels. The steering angle should be control with fast response speed, precise and controllable angle, and a change of the steering angle should be as smooth as possible to avoid sudden shake of vehicle. Accordingly, the steering angle control motor has a two-way operation function, a precise and controllable rotation angle, smooth operation, fast execution speed, great reliability, as well as a compact structure and convenient layout. Preferably, the steering angle control motor is a direct current (DC) servo motor. A motor terminalis configured to provide a DC power supply and a corresponding control signal to the DC servo motor.

As shown in, an output end of the steering angle control motor is provided with a mounting flange. The steering angle control motoris fixed on the first housingthough a connecting boltand a gasket, and an axis of the steering angle control motoris parallel to an axis of the first housing. The motor shaftof the steering angle control motoris connected to the input shaftof the speed-reduction mechanism through the shaft coupling, so as to achieve power transmission.

As shown in, the input shaftof the speed-reduction mechanism includes the pinion gear. The pinion gearis fixed on the input shaftby key connection. Deceleration and torque increase can be realized through the gear wheel. In an embodiment, the gear wheel is integrally formed with the first half shaftin the differential mechanism assembly, that is, power output by the steering angle control motoris subjected to deceleration and then directly transmitted to the first half shaft. The first half shaftis in splined connection with a first half shaft gear, such that the power output by the steering angle control motordirectly acts on the first half shaft gear of the differential mechanism assembly. The first electromagnetic clutch and the second electromagnetic clutch are controlled to be in a disengaged or energized state, so as to control a power flow process in the differential mechanism assembly to realize the steering mode and the braking mode.

As shown in, the traditional bevel gear differential is modified to obtain the differential mechanism assembly. The differential mechanism assembly includes a differential housing, a first half shaft, a first half shaft gear, four spur bevel planetary gears, a universal joint, a fourth connecting screw, a second half shaft. a second half shaft gear, a spherical gasketand a thrust gasket. Four shaft journals of the universal jointare respectively embedded in four grooves of the differential housing. The four spur bevel planetary gearsare sleevedly provided on the four shaft journals of the universal joint, respectively. The four spur bevel planetary gearsare engaged with the first half shaft gearand the second half shaft gear. A shaft journal of the first half shaft gearis supported in a hole at a first side of the differential housing; and a shaft journal of the second half shaft gearis supported in a hole at a second side of the differential housing. The first half shaft gearis in splined connection with the first half shaft. The second half shaft gearis in splined connection with the second half shaft.

As shown in, a clutch housing of the second electromagnetic clutchand a corresponding gasketare fixed on the differential housingthrough a fifth connecting screw. The differential housingand the clutch housing of the second electromagnetic clutchare mounted in the second housingthrough a pair of angular contact ball bearings. A power supply line of the second electromagnetic clutchis connected from a slip ring at an end of the differential housingthrough the second housing. The first electromagnetic clutchis configured to control the connection between the differential housingand the housing assembly. When the first electromagnetic clutchis in a de-energized state, the differential housingand the housing assemblyare fixedly connected, that is, the differential housingis not rotatable. When the first electromagnetic clutchis in an energized state, the differential housingand the housing assemblyare disconnected, that is, the differential housingis rotatable in the housing assembly.

As shown in, the first electromagnetic clutchmainly includes a clutch housing, a first torque adjusting ring, a first spring supporting base, a first spring locating ring, a first spring, a first friction sheet, a first armature, a first magnet yokeand a first electromagnetic coil. As shown in, the clutch housing of the first electromagnetic clutchis fixed on the housing assemblythrough the second connecting screwand a corresponding gasket. In an embodiment, six second connecting screwsare evenly and circumferentially distributed. The first magnet yokeand the first electromagnetic coilare fixed on the clutch housing of the first electromagnetic clutch.

In an embodiment, the first torque adjusting ringis axially and threadedly fixed on the first half shaft, that is, a corresponding connecting portion of the first half shafthas external thread to allow the first torque adjusting ringto rotate on the first half shaft. In an embodiment, the first spring locating ringis circumferentially fixed to the first half shaftwith a wedge key. The first spring locating ringand the clutch housing of the first electromagnetic clutchwork together to circumferentially locate the first spring. In an embodiment, one end of the first springis supported on the first spring supporting base, in which the first spring supporting baseis arranged at a groove of the first torque adjusting ring; and the other end of the first springpresses against the first armature. As shown in, a portion of the differential housingextending out from the second housingis also a part of the first electromagnetic clutch. The portion of the differential housingextending out from the second housingis provided with spline grooves, and is in splined connection with the first armature, such that the first armaturecan axially slid on the portion of the differential housing. In an embodiment, the first friction sheetis fixed on the second housingthrough connecting screws arranged evenly and circumferentially, and a power supply line of the first electromagnetic clutchis directly connected from the clutch housing of the first electromagnetic clutch.

In an embodiment, referring to, when the first electromagnetic clutchis in a de-energized state, the first armatureis pressed against the first friction sheetof the second housingunder the action of the first springto lock the differential housing. When the first electromagnetic clutchis in an energized state, the first electromagnetic coilgenerates an electromagnetic force to allow the first armatureto slide axially along a splined portion of the portion of the differential housingextending out from the second housing. Then, the first armaturepresses against a tail end of the splined portion to disconnect the second housingand the differential housingto enable the differential housingis to rotate freely.

In an embodiment, the first torque adjusting ring, which is threadedly connected to the first half shaft, can rotate to change an initial pression of the first springto change a pre-tightening torque of the electromagnetic clutch. Consequently, a reduction of operating torque of the electromagnetic clutch of the dual-mode active rear-wheel steering device due to gradual wear of the friction sheet during operation can be overcome, leading to more reliable the dual-mode active rear-wheel steering device.

As shown in, the second electromagnetic clutchmainly includes the clutch housing, a second torque adjusting ring, a second spring supporting base, a second spring locating ring, a second spring, a second friction sheet, a second armature, a second electromagnetic coiland a second magnet yoke. Connections between the parts of the second electromagnetic clutchare almost similar to those of the first electromagnetic clutch. Differences are that the clutch housing of the second electromagnetic clutchis fixedly connected to the differential housingthrough the fifth connecting screwand a corresponding gasket; and the second friction sheetis fixed on the clutch housing of the second electromagnetic clutchthrough connecting screws arranged evenly and circumferentially. In an embodiment, the second armatureis slidably sleeved on the second half shaftby splined connection. The power supply line of the second electromagnetic clutchis connected from a slip ring at an end of the clutch housing of the second electromagnetic clutchthrough the housing assembly. When the second electromagnetic clutchis in a de-energized state, the second armatureis allowed to axially move along a splined portion of the second half shaft, and is pressed against a tail end of splined portion of the second half shaftunder the action of the second spring, such that the second half shaftand the second electromagnetic clutchare disconnected, and the second half shaftis rotatable. When the second electromagnetic clutchis in an energized state, the second electromagnetic coilgenerates electromagnetic force to press the second armatureon the second friction sheetfixed on the clutch housing of the second electromagnetic clutch, such that the second half shaftand the second electromagnetic clutchare fixedly connected, that is, the second half shaftrotates in the same rotation speed with the second electromagnetic clutch.

As shown in, the motion conversion mechanism converts motions through the inner cyclical ball-lead screw-nut pair, that is, a rotational motion of the steering angle control motor is converted into a linear motion of a lead screw of the motion conversion mechanism, such that the steering tie rod is driven to perform a linear motion, and the control of the steering angle of rear wheel is achieved.

In an embodiment, the first lead screwand the second lead screware the same in parameters except the rotation direction. Therefore, the dual-mode active rear-wheel steering device operates at a common steering mode when the first electromagnetic clutch and the second electromagnetic clutch are in the de-energized state, that is, the rear wheels steer in the same direction during operation, which is energy-saved, environmentally friendly and reliable.

As shown in, an output end of the first half shaftand that of the second half shafthave a drill way, which is a nut part of the inner cyclical ball-lead screw-nut pair. Inside the drill way is provided with an inner cyclical raceway, such that a ball can cyclically roll. A screw part of the inner cyclical ball-lead screw-nut pair is provided with a ring groove for the cyclically rolling of the ball, and forms the inner cyclical ball-lead screw-nut pair with the first half shaft and the second half shaft. In an embodiment, a portion of the first half shaftand that of the second half shaftextending out from the housing assemblyare provided with a felt ring for sealing. A dust-proof cover is configured for further sealing, in which one end of the dust-proof cover is fixed on the lead screw and the other end of the dust-proof cover is fixed on the housing assembly, such that the rear-wheel steering device is prevent from dust and pollution.

The dual-mode active rear-wheel steering device provided herein can realize the steering mode and the braking mode. When driving on a rough road, the dual-mode active rear-wheel steering device can be self-locked to avoid shaking vibration of rear wheels due to road impact.

The working principle of the dual-mode active rear-wheel steering device is described below.